Hello Guest!
Welcome to the official Square Foot Gardening Forum.
There's lots to learn here by reading as a guest. However, if you become a member (it's free, ad free and spam-free) you'll have access to our large vermiculite databases, our seed exchange spreadsheets, Mel's Mix calculator, and many more members' pictures in the Gallery. Enjoy.

Both zukes and spag squash are C. pepo so I believe they can cross pollinate. I'm in a similar situation - I have 6 different types of squash, and 5 of them are C. pepo. My plan is that if I have more than one type of squash flowering, I'll manually pollinate the flowers and then tape them shut. No need to remove the tape - it will fall off with the flower. The ideal time to manually pollinate is the first morning that the female flower is open. Now for the disclaimer, this will be my first year trying this and it's based on internet research. (So, it might work...or it might be another one of those "lessons")

I can't remember recommended distance to prevent cross pollination but it seems like it was several hundred feet. I planted a zuke and a yellow crookneck about 6 feet apart two years ago. It produced one squash that was yellow on one end, green on the other. I'm assuming that was from cross pollination, but I really don't know.

There is a lot of info on the internet and youtube about manually pollinating squash. They also will help you identify the male vs female flowers.

I've planted summer squash and zucchini in the same bed with no problems. jillintx, I wonder if that yellow & green squash was one that got into a seed pack by mistake- I have seen where you can order seeds for a squash that looks just like you described- 1/2 yellow, 1/2 light green.

As a rule, cross pollination only affects NEXT year's crops if you save and use the seeds from the fruit. It shouldn't affect the current harvest. Squash will be their variety as planted, summer being summer and winter being winter.jillintx......I've seen that squash that's two colors, also. Its named Zephyr with a yellow top (but the knob is green) and a green fatter bottom.

Maybe I did have a stray seed. It's hard to say because I only got one squash that year, so I can't say if others would have been the same. I also can't remember if it came from the zuke plant or the yellow squash plant. I just remember being disappointed by the whole squash process.

I am glad to know that I'll only need to do the manual pollination on the squash that I want to save seeds. Thanks for clearing that up.